Gem of the Month

Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

Go to: Homepage -- what's new at ACS -- monthly specials and discounts -- "buried treasures" -- BWS/FS jewelry designs -- gem topic of the month -- gem topic archive -- birthstones -- ask Barbara -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- setting these gems -- free gemology course

 

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Chrysoberyl

Chrysoberyl has suffered a lack of recognition for its own merits, as its two famous siblings get all the attention. Alexandrite, which is color change chrysoberyl, and the phenonmenal cat'seye chrysoberyl, are justly appreciated for their rarity and beauty, and they will be featured in future essays. The name "chrysoberyl" comes from Greek roots for "golden" and "containing beryllium". This gem is NOT a part of the beryl family of gems (aquamarine, golden beryl, red beryl, Goshenite, emerald) which are beryllium aluminum silicates -- while chrysoberyls are beryllium aluminum oxides.

Daylight Incandescent

[Alexandrite (color change chrysoberyl)]

[Cat'seye chrysoberyl in honey brown, the most highly prized shade]

Transparent gem chrysoberyl comes in a limited array of colors from pure yellow through shades of yellow green to green to brownish yellow, to brown: iron is the coloring agent. It is a superior jewelry stone. Its hardness at 8.5 (nearly equal to corundum) and its lack of cleavage give it excellent durability. Its high refractive index and polish luster make a well cut specimen nearly the equal of a diamond in brilliance.

[Faceted chrysoberyls in the most common colors: shades of yellow]

Shades of yellow are more common than yellow green or green. Premium prices accrue to stones that achieve yellow - green or green color with strong saturation. There is an extremely rare form of chrysoberyl colored by vanadium that is vivid emerald green.

[Desirable chrysoberyls showing yellow-green to green color]

The Spaniards and Portuguese of the 18th and 19th centuries, were big appreciators of this stone (which they called chrysolite) and many historical jewelry pieces with this gem have been found in shipwrecks and can be seen in museum collections. Major sources are Russia, Sir Lanka, Brazil Zimbabwe, Tanzania, and Madagascar. As the demand is small, there is no vigorous mining taking place, but good reserves of the gem are available should it increase in popularity.

No special care is necessary with this gem which can be steam or ultrasonically cleaned, and is stable to light, heat and chemicals. As such, and considering its durability it is a good choice for a man's ring or an "everyday" ladies ring.

Almost always faceted due to the exceptional brilliance an occasional cabochon is cut and makes an interesting piece.

[Rarely seen: a chrysoberyl cabochon -- would make a great ring stone!]

There although Alexandrite has been made in synthetic form by a very high technology and expensive process, and it is no doubt possible to make synthetic yellow chrsoberyl, the economics prevent its entering the marketplace at this time since clean natural stones are available at reasonable prices.

The crystal habit of this gem tends to flattened tabular crystals, but a tendency to form contact and penetration twins can occasionally result in a repeating hexagonal radial crystal called a trilling which is much admired by mineral specimen collectors.

[Chrysoberyl twinned crystal "trilling"]

It is sometimes mined at primary sites from pegmatites, and in these locations often found in conjunction with beryl and quartz. It is more often recovered from secondary alluvial deposits (gem gravels) containing spinel and corundum.

Value

Clean, saturated, yellow and yellow-green and particularly yellowish green stones in larger sizes are most highly prized. Pale yellow, yellow brown and brownish pieces have lower value. Custom cuts add substantial value as the vast majority of chrysoberyl gems in the marketplace are native cut.


Gemological Data:

Makeup: Beryllium aluminum oxide

Luster: Vitreous to subadamantine

Hardness: 8.5

Crystal structure: Orthorhombic

Fracture: splintery to granular

Cleavage: none

Density: 3.71

RI: 1.74-1.75

Birefringence: .009

Pleochroism: weak to moderate, different shades of body color

Dispersion: .015


Stones Currently Available:

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Go to: Homepage -- what's new at ACS -- monthly specials and discounts -- "buried treasures" -- BWS/FS jewelry designs -- gem topic of the month -- gem topic archive -- birthstones -- ask Barbara -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- setting these gems -- free gemology course